Sheet metal Steel joists of a wide variety have been proposed for erecting floor structures. Usually such joists are used to replace wooden joists. Sheet Metal joists having solid webs have been used, but the webs interfere with the space between the floor and the ceiling beneath. Such joists usually were formed as of sheet metal as a C-section, ie there was a central web, and the opposite side edges of the web were formed into edge flanges. Several such bends were sometime incorporated in an effort to get greater strength, while using thinner gauge sheet metal. Services such as plumbing wiring and HVAC were obstructed by such joists Accordingly metal joists have been proposed which are formed with openings, usually generally triangular or trapezoidal openings, in the web, while the two edges of the joists were formed with bends, as before. These openings were positioned so as to define diagonal struts extending across the joists. In this way it was hoped to achieve strength while reducing weight and obstruction. However because the openings in the metal joists were of these specialized generally triangular or trapezoidal shapes, the services, in many cases conduits of substantial diameter, could not fit through the openings. It was not possible for the builder to cut away any of the diagonal struts to provide larger openings for services, since this would drastically reduce the strength of the sheet metal joists.
The shape of these openings tended to restrict the size of the conduits which could be passed through the joists.
Another problem arose in that the triangular openings were formed with edge flanges around their perimeter. Where these edge flanges extended around an angular corner of the opening there was a tendency for the sheet metal to crack. Consequently the corners had to be radiussed or rounded out. This meant that there was more metal at each of the corners, and the size of the openings was reduced. Another problem arose in cutting these joists to length. The openings were arranged in pairs with one triangle facing one way and the next triangle facing the opposite way. Cutting such joists to length requires that all of the openings of a particular orientation, in all of the adjacent joists in a floor, shall line up. This was required to facilitate passing of services through the openings in the joists. However due to the alternating orientation of the triangular openings this requirement resulted in cutting off end portions of sheet metal joists equal in length to the space occupied by two of the openings, in many cases. Forming such sheet metal joists with alternating triangular openings, requires that the openings be formed repeatedly along the joist. However at each end, the joist web must be a solid piece of sheet metal and free of openings. This required specialized machines which could punch the openings in the sheet metal, repeatedly but which could be controlled so as to “miss” one or more openings, leaving a length of the sheet metal web, solid, and available for cutting to length.
Another factor is that concrete is in wide use for pouring a floor slab.
Usually the slab was simply supported on top of the joists. It is now found that when portions of the metal joists are partially embedded in the concrete, they provide much greater strength to the slabs. Slabs can thus be thinner than in the past, saving material, time, and weight.
It has now been surprisingly found that the use of the specialized triangular or trapezoidal shapes of these joist openings, is unnecessary.
Reduction in weight is possible, by the use of the invention, it is possible to make sheet metal joists with regular symmetrical generally oval-shaped openings, with end portions of the opening being defined by a semi-circular radius. The remainder of the opening is defined by opposite parallel linear edges.
The resulting openings are thus of a somewhat extended oval shape, with linear sides. Solid portions of the sheet metal web remain, between adjacent openings and form sheet metal struts extending transversely from one edge to the other of the web. This avoids the diagonal struts of earlier joists. This also means that the size of the conduits passed through the openings can be increased. The openings substantially span the distance across the web, between the edge flanges of the joist. By the use of the invention it is now possible to form sheet metal joists with openings which can accept conduits having a diameter equal to the distance across the web opening between the edge flanges of the joist.
This is a great improvement over the earlier triangular opening and diagonal strut configuration.
Openings with semi-circular or radiussed ends avoid the problems caused by the corners of the triangular or trapezoidal openings and splitting of metal, and results in a much stronger joist. The use of openings with semi-circular ends greatly facilitates high speed manufacture of such joists. The openings are of identical footprint along the sheet metal web. This means that cutting the sheet metal joist to length becomes possible at shorter intervals, and there is less joist length lost in the process.
The joists with such openings define service pathways for cylindrical service conduits. In each joist the conduit diameter can be equivalent to the distance across the joist between one side edge of the opening and the other, transversely across the joist. This means that the conduits can pass through any opening in the joist, regardless of the orientation of the opening in the joist. This greatly reduces wastage of sheet metal during manufacture.
Much larger conduits can be accepted.
Another factor is earlier designs was the thought that it was essential to remove as much metal as possible. This was considered desirable to improve acoustical performance and avoid transmission of sound from one floor to the next. It has now been found that this was incorrect and unnecessary, at least for making sheet metal joists. What is required is a joist with openings which leave larger openings and more symmetrical openings without loss of strength. It has also now been found that the opposite parallel linear edges of each opening can be greatly strengthened by removing less sheet metal at each opening, rather than more. This surprising development results in leaving an additional piece of sheet metal along side each of the linear edges. These additional pieces are formed, in accordance with the invention, into two generally right angular bends, resulting in two additional U-shaped reinforcing channel structures along the opposite linear sides of each opening in the joist. Preferably both right angular bends are formed spaced apart from each other, so as to define a U shaped reinforcing channel with side walls in parallel planes spaced from one another, and a web at right angles to the side walls extending between the side walls. This greatly reinforces and increases the strength of the joist in the critical area of the extended linear edges of each opening. The fact that more metal remains in the joist does not cause either thermal or acoustical problems, since the extra metal, which is not removed, is simply displaced in a location alongside the opening.
The blanks of sheet metal removed in this process, are of a size and shape which leads to economies in the process since the blanks are smaller. Slug ejection problems in the manufacturing machinery are reduced and there is less wastage of metal.
The semi-circular ends of the openings reduce the problems for the builder who wishes to pass service conduits through the joists within the floor. Much larger diameter conduits can now be fed through the joists, than was possible before. This leads to less sales resistance due to a greater acceptance of the product in the market place.
The shape of the openings is symmetrical and identical.
All the various edges and U shaped reinforcing channels are formed on one side of the sheet metal, leaving the opposite side of the sheet metal smooth and unobstructed and planar. This makes it possible to align the joists in pairs and to place them back to back, with their smooth planar sides in contact with one another, and with their respective edges and U shaped reinforcing channels extending outwardly on opposite sides of the pair of joists.
This arrangement makes stronger composite joists while still maintaining the full size of the openings through the joists, for passing services.
These features can be used in joists having special embedment edge formations for embedment in concrete.
The features can also be used in forming much heavier duty joists with the edge formations formed into a triangular tube shape.
Such joists enable to formation of a floor system with rim members located on a wall structure, and with the joists extending across the space between opposite rim members.
The rim members will also be formed with openings of the type described above. Such rim members will also provide support flanges for supporting opposite ends of the joists. Where a concrete slab floor is to be poured such rim members will incorporate embedment formations for embedment in the slab.
Fastening tabs extend from the rim members, for fastening to the ends of the joists. Abutments may be formed on the rim members to engage opposite sides of the web of each joist to give greater strength.
It will be appreciated that this sheet metal joist, which improves on all these problems associated with prior joists, will have application in general use, for many various construction applications. In particular however it will have advantages in the construction of floors with joists acting as reinforcement for thin-shell concrete slabs.
Such joists can also be used to form floors having a panel surface such as plywood panels.
The joists and rim members may be associated together in accordance with the method described. Preferably the assembly of the rim members and joists, and also the pouring of concrete in some cases, will be done in a factory away from the building site. The floor can be prefabricated in sections, with each section being a composite of a concrete panel, with sheet metal joists embedded by their edges in the panel, and giving it reinforcement. When transported to the site the composite floor sections or panels will simply be lifted into place and fastened together to form the complete floor in the building.